There are four major types of cartilage in mammals. Hyaline cartilage is the only type of cartilage covered by this current invention, and a brief description of why it is different from the other three types of cartilage is necessary, to help the reader understand the invention and compare it against the prior art.
Hyaline cartilage is the main type of cartilage that provides smooth, slippery, lubricated surfaces that slide and rub against other cartilage surfaces in “articulating” joints, such as knees, hips, shoulders, etc. It is formed as a relatively thin layer (usually no more than about 3 or 4 millimeters thick) that covers certain surfaces of hard bones. While the hyaline cartilage in some joints (such as fingers) is not heavily stressed, the hyaline cartilage in other joints (notably including knees and hips) is frequently and repeatedly subjected to relatively heavy compressive loads, shear forces, and other stresses, and it does not have a blood supply or cellular structure that enables the type of cell turnover and replacement that occurs in most other tissues. As a result of those and other factors, hyaline cartilage in knees and hips needs repair or replacement at fairly high rates among the elderly (due to gradual wear, injury, disorders such as osteoarthritis or rheumatoid arthritis, etc.), and at lower but significant rates among younger patients (due to injury, congenital joint displacements that lead to unusual wear patterns, etc.).
Since this invention relates to fiber reinforcing layers for hydrogel components of implants, it is important to recognize that hyaline cartilage is present only in relatively thin layers that coat the surfaces of bones. Since it is a soft tissue that cannot repair itself, it is vulnerable to damage when subjected to repeated loadings and stresses, and it would be even more vulnerable to damage if it were present in thick layers. As a result, the fiber reinforcing layers disclosed herein are subjected to crucially important constraints, when it comes to thickness.
Meniscal cartilage refers to specialized arc-shaped segments that help stabilize the knee and shoulder joints. Like hyaline cartilage (and unlike elastic cartilage or spinal cartilage), they have smooth lubricated surfaces that slide and rub against other cartilage surfaces, when a joint is moving. They are made of a highly fibrous form of cartilage, which is affixed to hard bone mainly via long fibers that extend out of the tips of the arcs, while the peripheral surfaces of the arcs are affixed to soft tissues instead of bone. In the shoulder joints, these arc segments are called labrum (or labral) segments; however, since their shapes and structures are nearly identical to meniscal segments in knees, and since labral cartilage in shoulders need to be repaired only rarely compared to meniscal cartilage in knees, labral cartilage usually is included in the term “meniscal cartilage”.
Because of their arc shapes, meniscal cartilage segments have roughly triangular cross-sections, and their center regions have greater thickness than the hyaline cartilage layers that cover the surfaces of bones in joint regions. While the methods disclosed herein can be adapted to enable the creation of all or at least a portion of a three-dimensional fiber array that will have the proper shape and thickness for reinforcing a meniscal segment (indeed, early prototypes have been created with such shapes, which appear to be satisfactory for such use), the focus of this invention at the current time and as disclosed herein is on creating three-dimensional fibers arrays that have suitable thicknesses for reinforcing the relatively thin layers that characterize hyaline cartilage.
This invention specifically excludes two other types of mammalian cartilage, which have very different sizes, shapes, and structural requirements than hyaline cartilage (or meniscal cartilage). A brief discussion of those two excluded types of cartilage can help the reader better understand the invention, the obstacles it must overcome, and why a number of items of prior art, developed for those other two types of cartilage, become irrelevant and even misleading when considered in the context of attempts to repair hyaline cartilage.
In particular, the spinal discs (which separate the vertebral bones) are made of a completely different type of cartilage, and they have no smooth and slippery surfaces. Instead, the spinal discs must completely prevent any sliding or “shearing” motions between adjacent vertebral bones, since any such sliding motions could pinch and severely damage or even sever the spinal cord. Therefore, the cartilage in the spinal discs is heavily reinforced by long fibers that emerge from the vertebral bones and penetrate essentially all the way through each spinal disc. In addition, the spinal discs are substantially thicker than hyaline cartilage segments. Both of those factors enable the manufacture of strong reinforced implants for repairing spinal discs, in ways that are simpler and easier than providing adequate reinforcing layers that must be kept thin and that cannot have any roughness on a smooth and lubricated surface. In repairing a spinal disc, the real challenge is in protecting the spinal cord, rather than in providing adequate materials for replacing the disc. This is reflected in the fact that spinal discs are repaired by neurosurgeons, while joint cartilage is repaired by orthopedic surgeons.
Elastic cartilage (i.e., the type of cartilage that gives shape to certain body parts such as the ears and nose) also is very different from hyaline cartilage, in both structure and function. Unlike cartilage in joints, elastic cartilage is not subject to wear and degradation; nevertheless, it sometimes needs to be repaired, usually to reshape ears or noses that were injured in accident victims, burn patients, etc. Elastic cartilage does not need to withstand any significant compressive or shearing loads or stresses, so implants for repairing elastic cartilage only need to meet low and minimal requirements for strength, toughness, and durability. In addition, elastic cartilage does not have smooth sliding surfaces that must be carefully protected.
Accordingly, only a set of very low and relaxed structural and physical requirements apply to elastic cartilage, compared to hyaline or meniscal cartilage in load-bearing joints such as knees. That set of very low mechanical and strength requirements has led to extensive research in regenerating elastic cartilage in ears and noses, using transplanted cells that are temporarily protected by synthetic implants that are designed to be digested, resorbed, and replaced by natural tissue during a span of several months following surgical implantation.
However, two factors can help illustrate and explain the problems that make hyaline cartilage repair, in dynamic joints, much more difficult than elastic cartilage repair, in inert and non-stressed locations such as an ear or nose.
The first factor is this: in hyaline cartilage in “loaded” joints such as knees, chondrocyte cells will not actively secrete the “building block” molecules that are assembled into cartilage, unless they are “activated” by stresses imposed on the bones. Compressive stresses in particular trigger certain signaling mechanisms, which cause chondrocyte cells to respond by secreting the building blocks of cartilage.
However, implants that carry transplanted cells must be very careful about imposing compressive loads on the implants. Such implants need to be at least somewhat soft and non-rigid; otherwise, they would scrape, abrade, and damage any opposing cartilage surfaces they rub against. However, if compressive loads are imposed on a soft and non-rigid implant carrying transplanted cells, the compressive loads will pose major risks of damaging the implant, by squashing and killing the cells in the implant, or by squeezing the cells out of the implant.
This leads to a difficult balancing act. Despite the best efforts of many hundreds of researchers and surgeons, implant devices carrying transplanted cells can be used to regenerate hyaline cartilage, only when relatively small defects (usually caused by physical injuries) are involved. Furthermore, because recovery and rehabilitation is slow and gradual, and requires months after surgery is performed, cell transplant approaches usually are considered as an option only if a patient is relatively young (such as under the age of about 55 or 60), and is not carrying substantial excess weight. This eliminates most people older than about 60, and people who are overweight, as candidates for cartilage repair using cell transplantation. That creates major limitations, since patients older than about 60, and patients who are overweight, comprise the very large majority of people who suffer from serious cartilage problems in their knees and hips.
A second obstacle that arises, in repairing hyaline cartilage in moving joints, involves the eventual fates of “resorbable” implants, which are made of specialized materials (such as poly-glycolic acid combined with collagen fibers) that are slowly digested and dissolved by enzymes in body fluids, over a span of months. This type of digestion and replacement enables resorbable implants to be gradually replaced by natural tissue, which is almost always preferable to a synthetic foreign implant, where feasible. However, biological resorption and replacement can lead to the release of fragments and debris, after a synthetic material passes a midway point of being partially broken apart and digested by enzymes. In an inert location such as a segment of elastic cartilage in a nose or ear, such fragments and debris will not cause serious problems. However, if fragments and debris from a partially-resorbed implant were released into a moving joint such as a knee, they might begin abrading and damaging the smooth cartilage surfaces that are pressing, sliding, and rubbing against each other.
It may be possible to overcome these problems, if certain types of reinforcing fiber materials in combination with resorbable hydrogels are used. For example, one approach that holds potential is to make a reinforcing fiber array from non-resorbable fibers that are biocompatible and that can encourage cell growth within the fiber array, while making the hydrogel from a material that can be dissolved and replaced. An enormous amount of research is actively being done on “tissue engineering”, using in vitro cell culturing methods, devices, and reagents to grow cells outside the body, but within matrix-type materials that will enable cell-carrying implant devices to be implanted into a body. Therefore, the current invention focuses upon and is limited to nonresorbable 3D fiber arrays, which have been or can be coupled to bone-anchoring devices that are designed to last for decades (preferably for the entire remaining life of any patient); however, the hydrogel material itself, which will need to be reinforced by a 3D fiber array as described herein, is not limited to nonresorbable synthetic hydrogels only, and might be provided by collagen, polyglycolic acid, or other types of resorbable fibers or polymers.
In view of the major differences between hyaline cartilage versus spinal or elastic cartilage, it must be understood that: (i) efforts that have been made to repair elastic or spinal cartilage cannot be simply or readily adapted to repairing hyaline cartilage, which must overcome very different problems and operating constraints in joints such as knees or hips; (ii) all discussion and claims below, and all subsequent references to cartilage herein, are limited solely to hyaline cartilage; and, (iii) all references herein to implants are limited to nonresorbable synthetic implants for replacing hyaline cartilage.
In addition, all teachings and claims herein are expressly limited to surgical implants that contain hydrogel components. To qualify as a hydrogel, a material must have the types of physicochemical properties that are regarded as “gelatinous” by people skilled in materials science. That term refers to a type of semisolid resilience that is different and distinct from (for example) a piece of fabric or sponge that has been saturated with water. Although fabrics, sponges, and various other materials can enable the passage of water molecules through those materials, they do not have the type of structural properties or physical and mechanical traits and behavior of gelatinous materials.
Most hydrogels that have substantial tensile strength (which are the only hydrogels of interest herein) hold water molecules within a cohesive polymeric molecular matrix, in a way that enables the travel of the water molecules through the molecular matrix. Although such hydrogel materials must have at least some degree of deformability, they cannot be in liquid form, and they must return to a specific nondeformed shape after any loads or stresses have been removed. A different class of colloidal suspensions (often called “thixotropic” materials) can also form hydrogels when allowed to sit in stationary form, but they do not have substantial tensile strength, and they will convert into liquids if subjected to shearing stresses, so they are not of interest herein.
In natural cartilage, the hydrogel structure is created by a three-dimensional matrix that is given shape and strength mainly by collagen, the fibrous protein that holds together nearly all soft tissues in animals. In synthetic hydrogels, the three-dimensional matrix usually has a molecular structure made of complex polymers that have a combination of: (i) long continuous chains (often called “backbone” chains), containing mainly carbon atoms and sometimes containing oxygen, nitrogen, sulfur, or other atoms as well; (ii) side chains, which branch off the “backbone” chains in ways that can have either controlled or semi-random spacing, length, content, etc.; and, (iii) crosslinking bonds, which connect the backbone and side chains to each other in ways that create complex three-dimensional molecules that have sufficient spacing between them to allow water molecules to travel within the molecular matrix.
Synthetic hydrogel polymers must be hydrophilic, to cause them to attract and hold water molecules. This can be accomplished by including large numbers of oxygen atoms (usually in hydroxy groups), nitrogen atoms, or other non-carbon atoms in the backbone and/or side chains, to provide “polar” groups that will attract water, a polar liquid. This aspect of polymer chemistry is well known, and hydrophilic formulations of various candidate polymers are well-known and available.
Fluid permeability (which involves the ability of water to pass through the molecular matrix of cartilage) is important in the behavior and performance of natural cartilage. As an example, FIG. 6 in U.S. Pat. No. 6,530,956 illustrates how fluid flow through cartilage can help distribute and “smooth out” the peak pressures that are imposed on cartilage in a load-bearing joint such as a knee, when a person begins walking or running.
Even more importantly for the purposes of this invention, synthetic hydrogel polymers are flexible, and can be rolled into cylindrical forms that can be inserted into a joint that is being surgically repaired, via a minimally-invasive incision, using an arthroscopic insertion tube. By avoiding and eliminating the need for “open joint” surgery, arthroscopic insertion of a flexible implant in a rolled-up cylindrical form can spare surrounding tissues and blood vessels from severe damage during the surgical operation.
Due to these and other factors, hydrogel materials are of interest in joint repair implants, and may be able to provide better performance than the solid plastics (such as high molecular weight polyethylene, abbreviated as HMWPE) that are used today in most hip and knee replacements.
However, because water molecules make up a substantial part of their volume and weight, hydrogels are substantially weaker than solid plastics that do not contain any water. Accordingly, hydrogels have not been strong enough or durable enough, in the past, to offer realistic and practical alternatives to hard plastics, for use in implants for repairing or replacing hyaline cartilage in joints such as knees or hips.
The foregoing statement needs to be qualified, by mentioning a specific type of surgical implant that is available in Europe and Canada, but not in the United States. These implants are sold by a company called SaluMedica (Atlanta, Ga.), under the trademark SALUCARTILAGE. They are described in the SaluMedica website (www.salumedica.com) as being made from the same class of polymers in flexible contact lenses, but with denser formulations having greater strength. It appears that these implants are made in cylindrical shapes only, with enough length (or thickness) to cause them to remain in place without requiring any additional anchoring attachments, if inserted into a properly prepared cylindrical hole that is created by a surgeon in the surrounding cartilage.
However, none of the supporting articles cited in the SaluMedica website could be located in a search of the database of the National Library of Medicine. Instead, other articles (such as Lange et al 2005 and Meyer et al 2005) were located which reported that serious problems have arisen when such implants are used, including dislodgement and/or apparently total destruction of such implants in some patients who receive them, apparently due to “the inadequate connection to the bone with risk of dislocation”. Apparently because of these limitations, statements on the SaluMedica website indicate that the company is not even attempting to obtain approval for use of those devices in the United States.
It must also be noted that the SALUCARTILAGE implants are available, only in the form of partial “plugs”, which must be inserted into a hole that is created by a surgeon, in the surrounding cartilage area. Whenever that type of “plug” approach is used, it creates a circular seam or juncture between (i) the outer top surface of the inserted synthetic plug, and (ii) the surrounding natural cartilage. This seam or juncture cannot and will not have the level of smoothness of a normal undamaged hyaline cartilage surface; instead, even under the best of conditions, it will have the shape of a small gap or trench, surrounding the artificial plug. Over a span of years or decades, any discontinuity in the surface of a “repaired” cartilage segment will pose a serious risk of abrading and damaging the natural cartilage surface that presses, rubs, and slides against the modified surface.
The only way to avoid that type of problem is by replacing an entire cartilage segment, rather than by inserting a plug into the middle of a cartilage segment (in the case of femoral runners, this can be done by a “unicompartmental” repair, but that still requires replacement of either an entire medial segment, or an entire lateral segment). The implants described herein, which are manufactured in relatively thin and wide sheets rather than small plugs, are ideally suited to enable the replacement of entire cartilage segments, rather than merely inserting plugs into holes that have been cut into surrounding cartilage segments.
Indeed, in most cases, the preferred procedure is to replace both of the two cartilage segments that rub against each other in a joint, in a single surgical operation. This preference arises from the fact that as soon as one cartilage surface becomes damaged, it loses its smoothness, and begins to abrade and damage the other cartilage surface that it rubs against. Accordingly, because any surgical operation inflicts damage on the tissues and blood vessels surrounding a joint (and causes pain and discomfort, and requires a rehabilitation period), it usually is better to replace both surfaces in a single operation, rather than repairing one damaged surface in first operation, and then have to repair a second damaged surface in second operation a short time later. Accordingly, the plug-type hydrogel implants being sold by SaluMedica (for sale only outside the US) are very different from the thin sheets being developed by the inventors herein.
The recent and ongoing efforts to provide improved hydrogel implants for replacing cartilage in joints by Mansmann (the first-named inventor herein) are described in U.S. Pat. No. 6,629,997 (“Meniscus-type implant with hydrogel surface reinforced by three-dimensional mesh”) and published applications 2002-0173855 (“Cartilage repair implant with soft bearing surface and flexible anchoring device”), 2002-0183845 (“Multi-perforated non-planar device for anchoring cartilage implants and high-gradient interfaces”), and 2004-0133275 (“Implants for replacing cartilage, with negatively-charged hydrogel surfaces and flexible matrix reinforcement”), all of which are available from the US Patent and Trademark Office website, www.uspto.gov. The contents of those published items are incorporated herein by reference, as though fully set forth herein.
Much of that work has focused on hydrogels made from a class of polymers known as polyacrylonitriles (abbreviated as PAN). This class of acrylic derivatives formed the main component of certain types of synthetic fibers that formerly were sold by the DuPont company, under the trademark ORLON™. Other known hydrophilic polymers, including various forms of polyurethane, also offer candidate materials for use in forming hydrogels with enough strength for use as described herein. These polymers can be formulated in ways that will create molecular matrices having gelatinous properties, when hydrated.
Because hydrogel polymers (which must, by definition, contain substantial quantities of water molecules) will inevitably be weaker than various known types of hard plastics that do not contain any free water, the work by Mansmann has focused on hydrogels that are reinforced by three-dimensional fiber arrays, made of synthetic fibers having high tensile strength.
One method of fabricating such 3D fiber arrays, which was identified in the above-cited patent applications, is a three-dimensional weaving method used by a company called TechniWeave (a division of Albany International), to create high-strength composite materials for applications such as aeronautics and astronautics. However, as that process was evaluated in more detail, it became clear that it is not well-suited for medical devices that will need to go through a long and extensive process of in vitro testing, animal testing, and human clinical trials, before any such implant can be approved for use in human patients.
A major problem arises from the fact the prototypes that will be made and tested, in in vitro and then animal tests, are likely to be modified somewhat, each time more data and performance results become available from a previous series of tests. If a 3D weaving process is used, each newly-modified prototype will incur relatively high setup and startup costs. This is comparable to the costs of manufacturing operations that use molding technology, in which a new set of molds must be created each time a customer wants to modify an item being produced, even if the modification is only minor.
Accordingly, even though the TechniWeave process (or other similar processes) may be well-suited for manufacturing large numbers of units after a final design has optimized, it is not well-suited for developing and testing a series of prototypes that will undergo multiple changes, as prototypes are designed, made, and tested, and then redesigned, modified, and tested again based on earlier results. Therefore, other methods for making candidate reinforcing materials, with lower overhead-type startup costs, had to be identified and evaluated.
Faced with that challenge, the first-named inventor (an orthopedic surgeon) identified and hired a consultant (the second-named inventor herein) who is an expert in fibers and textiles, and who has extensive experience in developing ways to make articles having substantial thickness and controllable shapes, as described in patents such as U.S. Pat. No. 4,719,837, U.S. Pat. No. 5,470,629, and U.S. Pat. No. 6,579,815, Patent Cooperation Treaty application WO 89-01320, and European patent EP 375729 (all invented or coinvented by Popper).
Before the results of their joint efforts (which led to the invention herein) are described, several concepts and terms needs to be established, in two very different fields: (i) the structure and arrangement of normal and natural biological cartilage, in healthy mammalian joints, and (ii) means for assembling fibers into fabrics, textiles, carpets, and other materials. The following subsections address those two areas.
Condyles and Collagen Fibers in Natural Cartilage
Any bone surface that is covered by a layer of hyaline cartilage is referred to herein as a “condyle”. However, it should be noted that this term is not always used consistently, by physicians and researchers. Some users limit “condyles” to the rounded ends of elongated bones; this clearly includes the long bones in the arms and legs, it usually but not always includes smaller elongated bones in the hands, fingers, feet, and toes, and it clearly excludes the cartilage-covered “sockets” in the ball-and-socket joints of the hips and shoulders. By contrast, other authors use “condyle” to refer to any bone surface covered by hyaline cartilage, including the socket surfaces in hip and shoulder joints. Since reinforced hydrogels as disclosed herein can be used to replace hyaline cartilage segments on any bone surface, the broader definition (which covers any bone surface covered by hyaline cartilage, including long bones, finger joints, socket surfaces in hips and shoulders, etc.) is used herein.
Any condylar surface contains a transition zone, called the subchondral layer or zone, at the interface between the hard bone and the cartilage. This transition zone strengthens and reinforces the cartilage, to ensure that the cartilage (which is relatively soft) is not simply pushed or scraped off the supporting bone when a joint is subjected to loading and shearing stresses. In the transition zone, large numbers of microscopic collagen fibers, firmly anchored in the hard bone, emerge from the bone in an orientation that is generally perpendicular to the bone surface at that location.
When rounded surfaces are involved, that direction is called radial; the surface-parallel direction at any point on a rounded surface is called tangential. For convenience, all descriptions and drawings herein assume that a bone surface is positioned horizontally, with a layer of cartilage resting above it and on top of it, and with the smooth articulating surface of the cartilage as the upper exposed surface of the structure.
When described in that orientation, as collagen fibers rise through the cartilage and approach the smooth articulating surface of the cartilage covering layer, they go through a rounded transition, and become tangential to the articulating surface of the collagen. This is shown in photographs (taken by electron microscopes) of collagen fibers in hyaline cartilage segments, which are available in sources such as Clark et al 1990 and 1991. The tangential orientation of the collagen fibers on the surface of the cartilage helps create and sustain a smooth surface on the cartilage.
Fibers, Yarns, Fabrics, and Fiber Arrays
This section briefly reviews a number of terms and concepts in the field of fibers, fabrics, textiles, and “fiber arrays”.
As used herein, “fiber” includes long flexible strands of material that are suited for weaving, knitting, or other assembly into fabrics, textiles, carpets, or other fiber arrays. Most synthetic fibers are manufactured with essentially round cross-sections, although that is not necessary. They can be cut into any desired length after manufacture, and they typically are manufactured in continuous lengths, which are stored on spools, cores, or similar devices to facilitate handling and use.
The term “yarn” refers to a bundle or other relatively cohesive cluster of fibers, in which the fiber bundle comprises a generally cylindrical but flexible enlarged strand. Most synthetic fibers used to make conventional fabrics, textiles, or carpets are too thin to work with efficiently, in “monofilament” form. Therefore, they usually are twisted, braided, or otherwise manipulated in ways that create larger aggregated strands, called yarns, which are easier to handle and work with than very thin individual fibers. However, some types of polymer fibers can be made in any desired thickness (comparable to monofilament fishing lines having a range of diameters and tensile strengths). Accordingly, references herein to “fiber” or “fibers” (or similar terms, such as threads, strands, etc.) can include monofilament fibers, yarns, or any combination of the two.
The term “thread” is used herein to refer to a strand of fiber (either monofilament, or yarn) that is affixed to a backing layer by means of stitching, and or that otherwise passes through an eye of a needle during a manufacturing operation. This term, which arises from the conventional “needle and thread” pairing, distinguishes threads from other fibers that are woven or knitted into a fabric.
A very broad term, used herein to refer to and include any type of material that is manufactured from fibers in a controlled manner, is “fiber array”. Array derives from the same word as “arranged”, and the two words have essentially the same breadth. Arrays can include any type of fabric, mesh, carpet, or other textile or similar material made of a fibrous material that is somehow arranged (or arrayed) in a desired and controlled manner. Some fiber arrays have a relatively flat and mainly two-dimensional form, such as a single-layer woven, knitted, or similar fabric. Other fiber arrays have three-dimensional shapes where substantial thickness is crucial to their performance, such as in tufted carpets. Still other fiber arrays sit at various midpoints in the range from very thin to very thick, as occurs with knitted fabrics made from yarns with substantial thickness. Fiber arrays also can be made by means such as chemical treatments (using glues, adhesives, etc.), energy input (such as heat or radiation to cause partial melting and bonding of some fibers), or mechanical means other than stitching or tufting (such as needle-punching, using air to form a layer of “batt” material on the surface of a screen, etc.), to fix and set an array of fibers into the cohesive structure of an array.
As used herein, the term “fabric” refers to a relatively thin and flat fiber array, of a type that can be created by means such as conventional weaving, knitting, etc. “Fabric” is intended and used herein to distinguish relatively thin, essentially two-dimensional sheets of material, from thicker materials.
Thicker materials, in which thickness (which might also be referred to as height, depth, or similar terms) plays an important role and is deliberately created by means that extend beyond methods such as conventional weaving or knitting, are referred to herein as “three-dimensional arrays” (abbreviated as 3D arrays). As examples, any tufted material (such as a carpet) is a 3D array, since tufts are deliberately designed to extend a significant distance above or below a backing layer. An embroidered or other stitched material that adds additional fibers to a backing layer will become a 3D array, if any steps are taken to use either: (i) fibers with sufficient thickness to add significant height or depth, above or below the backing layer; or (ii) processing steps to create stitches, loops, tufts, or other structures that extend a significant distance above or below a backing layer of flat fabric. Similarly, materials made by stacking two or more layers of fabrics (or fibers) on top of each other would be regarded as 3D arrays, rather than flat fabrics. A piece of flat fabric does not become a 3D array merely because it is bent, curved, or folded, especially if such steps are reversible; however, 3D arrays can have controlled shapes, curvatures, contours, etc.
The term “backing layer” (or backing material) is used herein to refer to a piece of fabric or other sheet-type material that undergoes a stitching, embroidering, tufting, gluing, or similar process that affixes additional fibers to the backing layer. In some cases, a sheet of plastic, paper, or similar material can be used as a backing layer; this can be useful, if the backing layer is to be dissolved and removed in a subsequent step, to create an embroidered item having an “open” structure. However, in most cases, a woven fabric is used, to minimize the risk that the backing layer might suffer from damage, distortion, or a loss of integrity due to repeated puncturing by a sharp needle.
Stitching refers to the process of using one or more needles to repeatedly push one or more fibers through a backing layer. Various types of stitching are known, and two important classes of stitched materials are referred to herein as “tufted” and “sewn” arrays. The difference between those two types of fiber arrays is explained below, after the basic operating mechanism of stitching machines has been explained.
Computerized Stitching Machines
Various types of stitching machines (including programmable computer-controlled and/or robotic stitching machines) have been developed, for uses other than this invention. Since these types of machines can be adapted for use as described herein, they need to be briefly reviewed.
The discussion herein focuses on a specific type of machine called an AMAYA™ embroidery machine, which is made and sold by a company called Melco (www.melcousa.com), a subsidiary of a company called Saurer (www.saurer.com). The AMAYA system is designed to be modular, allowing a person or company to buy or lease a single unit; later, the person or company can buy or lease additional machines and hook them up together, so that multiple units can work together to create exceptionally complex items. The trademark AMAYA is an acronym for the phrase, “as many as you add”, to emphasize the modular nature of these machines. These machines are illustrated and described on Melco's website, and they are readily available in both new and used models. Training courses and videos that can help operators learn to use them also are available (any references herein to “operator” refer to a person who has learned how to program instructions into the software that runs the machine, and how to run such a machine and keep it supplied with fabric and threads).
Melco's AMAYA system has become a standardized and widely-used system; however, it is not the only computer-controlled stitching machine that is known and available. Other computer-controlled stitching machines suited for home use have been developed by companies such as Pfaff, Bernina, Singer, etc., all of which have recognized that new and useful functionalities can be created, when people who work out of their homes are able to couple devices such as standard sewing machines, to home computers; in addition, much larger systems have been developed that are suited for use in factories.
Accordingly, the AMAYA system can be regarded as creating and occupying a midpoint, halfway between (i) a low-cost home system that can be created by coupling a standard home-type sewing machine to a home computer, and (ii) a large and expensive factory system. The AMAYA system is well suited for the purposes disclosed herein, and it has been used with very good results; however, any other type, brand, or model of computerized or robotic stitching machine can be evaluated, to determine whether it can be adapted for use as disclosed herein.
It also should be noted that terms such as computerized, computer-controlled, and programmable are used interchangeably herein, and refer to any system that can be controlled by a set of electronic instructions that can be entered into the control system by a trained operator. Such control systems include conventional computers, usually referred to by terms such as mainframe, server, desktop, laptop, or notebook computers. If desired, control systems that can operate computerized stitching machines also can use various types of smaller computerized devices, often referred to by terms such as “personal digital assistants” (including Blackberry, Palm Pilot, Treo, and similar systems), mini-computers, tablet computers, etc., all of which usually are provided with an interface system (called a “universal serial bus”, abbreviated as USB) that is designed to enable such units to interact with larger computers.
As yet another option, computerized control systems can use electronic devices that are often referred to as “dedicated” control systems. One class of “dedicated” control systems involves relatively small box-type devices, which are coupled to the machine that is being controlled, by one or more data cables. These types of “small box” control systems usually are provided with a touch-screen, keypad, readout panel, or similar components to enable data display and command inputs. One or more integrated circuits (IC's) are provided inside the box, and these typically are provided with specialized instruction sets, often written in proprietary computer code that is “burned” or otherwise loaded into one or more of the integrated circuits. Other types of “dedicated” control systems are physically mounted on or embedded within a larger machine, as part of the machine; this class of control devices is exemplified by the types of control panels that typically appear in photocopy machines, to allow users to control the number of copies, enlargement and collating options, exposure settings, etc. All of these types of electronic control systems, designed to receive and handle instruction sets that are input into the control system by a human operator, are well-known to those skilled in those particular arts.
Accordingly, the AMAYA machine offers a good example of a computer-controlled stitching machine that was never previously used for the type of use described herein, but which contains a sophisticated computerized control system that provides an operator with a good, flexible, and highly useful range of controllable operating parameters, which can be adapted for use as described herein.
When this type of machine is in use, a piece of backing material that is to be stitched (such as, for example, the chest area of a tennis shirt, the end of a towel, the corner of a handkerchief or scarf, the front of a baseball cap, etc.) is placed in a clamping and stretching mechanism. This mechanism draws the backing layer somewhat taut, in a manner comparable to a miniaturized, movable loom, but usually without stretching the backing layer to an extent that would cause distortion of an embroidered item, after the tension is released and the embroidered item is removed from the machine. The clamping mechanism can then rapidly move the backing layer in any horizontal direction, in a way that is controlled by software instructions that have been entered into the software that runs the machine.
A single sewing needle, which typically points downward, held by a reciprocating mechanism that moves only vertically when in use, is positioned above the backing material. The needle holder (and a threaded needle) move up and down. Each downward stroke causes the tip of the needle (carrying a strand of thread that has been inserted through the eye of the needle) to penetrate the piece of backing material. The backing material cannot be moved, during the portion of the cycle that continues for as long as the needle penetrates the backing material and remains engaged in it. The needle is then raised, disengaging the needle from the backing material while leaving a portion of the thread passing through the backing layer. The backing material is then moved to a new position by the holding mechanism, and the process is repeated, to create another stitch.
The loops of thread that are pushed down through the backing layer, by the needle, can be secured by any of several means. In one approach, often referred to as “interlock” stitching (which creates a type of structure illustrated in cross-section, in FIG. 1), a secondary fiber strand is used, which remains on the back side (or the bottom side, reverse side, underside, etc.) of the backing layer. In this method, an initial enlarged loop is created beneath the backing layer, from the primary stitching thread. A small spool-type device, called a bobbin, is passed through the temporarily-enlarged loop, by a mechanism that transfers the bobbin from a first holder to a second holder (this is sometimes called a “floating” bobbin system). The needle is raised, disengaging it from the backing layer, and the primary stitching thread is pulled tight, in a way that collapses the loop of thread and pulls it snugly around the “locking” fiber, which remains beneath the backing layer. The backing layer is then moved slightly, and the next stitch is created by repeating the same sequence steps, except that the bobbin is transferred back from the second holder, to the first holder; the bobbin simply reciprocates back and forth, between its two different holders, as additional stitches are created.
Other types of stitching use different methods to secure the stitches to a backing layer. For example, a small loop of secondary fiber that will remain entirely beneath the backing layer can be passed through each loop of the primary thread that is pushed downward (by a needle) through the backing layer. The primary thread is then pulled tight, in a way that tightens and secures it against the small secondary loop, beneath the backing layer. In this manner, a relatively simple threaded needle system that remains beneath the backing layer (rather than a more complex “floating bobbin” system) can be used to create the small secondary loops that will prevent the main stitches from unraveling. This approach also avoids the need to make initial loops, beneath the backing layer, that are large enough to pass a bobbin through.
In still other systems, no secondary fibers are used to secure the stitches to the backing layer. Instead, if a moderately thick thread having a significant degree of stiffness is used, the rounded “head” of each loop of thread will remain lodged in the backing layer, each time the needle is withdrawn from the backing layer. Subsequently, after the stitching operation has been completed but before the item runs a risk of being snagged, unraveled, or otherwise damaged, a layer of adhesive can be applied to the bottom side of the backing layer. When the adhesive cures and hardens, it will lock the stitches in place. This approach is used in tufted carpets, embroidered patches, and various other items.
As mentioned above, the backing layer cannot be moved, during each instant when a threaded needle (which can only move vertically, when in operation) has been pushed downward in a way that engages the backing layer. In some types of 3D fiber arrays, a substantial loop of material is created and allowed to remain on the bottom side of the backing layer. 3D fiber arrays created in this manner usually are called tufted arrays, to distinguish them from other types of stitched arrays that are called sewn arrays.
In most types of tufted materials, the “face” side of the material (i.e., the side of the material that will be exposed and visible during normal use, such as in a tufted carpet, once the carpet has been installed on a floor) will be created on the bottom side of the backing layer, during the stitching operation. When a tufting material is being manufactured, loop-grabbing mechanisms (usually called “loopers”) are often used to grab the tip of each loop, as each tuft or loop is being formed on the bottom side of the backing layer.
This type of manufacturing process can help ensure uniform tuft heights, as illustrated by the uniform thicknesses of tufted carpets that cover very wide areas. If other types of curved, looping, or other stitch designs are used, in which the stitches are not pulled tight, a mechanical device called the “presser foot” on an AMAYA machine can be adjusted, in ways that will create non-tightened but relatively uniform stitch lengths and/or heights. That device as adjusted by turning a rotatable wheel, rather than via a computer command.
Because of how tufted 3D fiber arrays are manufactured, the majority of the thread mass, in a tufted array, will be located on the side of the backing layer which the threaded needles could reach, only when they penetrated through the backing layer. Accordingly, since AMAYA and most other types of stitching machines use needle holders that are positioned above the backing layers, the tufted loops will be created on the bottom side of the backing layer, during the tufting operation. Subsequently, after the stitching operation has been completed, the stitched layer of material is removed from the machine, and it is then turned over, to position the tufted side (often called the “face” side) on the top side of the layer of material.
By contrast, in sewn 3D fiber arrays, the majority of the thread mass will be on the top side of the backing layer, and only relatively small loops of thread will be created on the bottom side.
In a tufted structure, in each and every tufting loop, the entry point (i.e., where a strand of thread is pushed downward through the backing layer, presuming that the needle holder is positioned above the fabric holder) and the exit point (i.e., where the loop of thread is pulled back upward, through the backing layer) must be at exactly the same location. The entry and exit points cannot be separated by even a single strand of fiber in the backing layer. This arises as an inevitable result of the way tufting loops are created. When a threaded needle is pushed through the backing layer (in a downward stroke, when an AMAYA or similar machine is used), the needle “engages” the backing layer. This means that the shaft of the needle effectively “locks” the backing layer in place for an instant, for as long as the needle shaft continues to engage the backing layer. When the needle is then raised, the thread being carried by the needle will necessarily pass through the backing layer in the same location where it entered. Because of how the needle engages the backing layer, there is no way for even a single fiber of the backing layer to somehow jump across the needle, from one side of the needle to the other side, while a single tufting loop is being formed by a single down-and-then-up stroke of the needle.
Subsequently, after the needle tip has been raised high enough to disengage it from the backing layer, the backing layer can then be moved again, and the next tuft can be created. However, that does not change a crucial fact about tufted structures: in a tufted material, the entry and exit points for any specific tuft must be in the same location, and cannot be separated by even a single fiber of the backing layer.
By contrast, in a sewn 3D array, the “frame of reference” is changed, in a way that causes the “entry” and “exit” points for each stitch to be defined differently. If the needle holder is positioned above the backing layer, then the “face” side of a sewn fiber array will be created on the top side of the backing layer (this is the opposite of tufted materials). Therefore, the “entry” point for each stitch is deemed to be the point where the stitching thread rises up through the backing layer, and begins its travel path across the important side (i.e., the face side, functional side, etc.) of the embroidered or otherwise sewn material that is being created. Accordingly, the “exit” point for any given stitch is the location where the stitch then travels back down through the backing layer, in a way that effectively removes the thread from the face side of the material. If desired, any single stitch can be caused to form a closed loop, in which the entry point and exit point will be the same. However, in most cases, there is no reason to do that, and instead, the backing layer will be moved slightly, each time the needle is raised above (and disengaged from) the backing layer. This will cause each stitch to travel (or “traverse”) at least some distance across the surface of the backing layer. Accordingly, as noted above, in a sewn 3D fiber array, the majority of the thread mass will be formed on the top side of the backing layer, and only relatively small closed loops of thread will be positioned on the bottom side. Because of how the needle engages the fabric during each downward stroke, the small loops of thread on the bottom side of the backing layer must have exactly the same entry and exit points, which cannot be separated by any strands of fiber in the backing layer, even if an “interlocking” thread is inserted through each loop by means of a floating bobbin.
The AMAYA system (and most other computer-controlled stitching machines that are not designed to be “dedicated” to only a certain specific and limited type of manufacturing operation) can be programmed to make either sewn or tufted 3D fiber arrays, by changing the control parameters for any particular prototype (or any “production run” that will make two or more copies of items having identical designs).
The AMAYA system also provides an entire set of spool-holders, which can provide different colors and types of threads to a set of needles. Only a single needle will be active at any time; however, sixteen different needle holders are provided in a typical AMAYA unit, and each needle can have its own supply of thread, from a dedicated spool. This was designed to enable multi-colored embroidery, using up to 16 different colors or thread types, and when it is time to change from one color to another, the machine can do so automatically, based on an instruction set programmed into the computer before the stitching operation commenced.
Entering a set of instructions that will control a prototype or production run is comparable to writing a document on word processing software, or filling in boxes on spreadsheet software. Word processing or spreadsheet software can provide options and guidance, but it will not control what is typed onto any pages, or entered into any blanks or slots. In the same way that anyone who learns to use a word processing program can write anything they want, anyone who learns to use the software that controls a stitching machine can use it to create embroidered depictions of anything they want (such as animals, spaceships, or team mascots, as just a few examples). To do this, the creator can take any of several approaches, which include: (i) creating a graphical drawing of such an item, using tools that are provided by any of various types of drawing programs; (ii) scanning a photograph of such an object, and digitally converting the scanned image into an instruction set that will create a similar image using colored threads on a backing layer; or, (iii) buying a “clipart” instruction set from a person or company that creates and sells images that have been drawn by artists and then converted into instruction sets designed for use in computerized stitching machines.
Online help, customer support technicians, and user support groups for AMAYA users are all available, via the Internet. Training materials and courses, and instruction books and videos, also are available for anyone who wants or needs to learn to use these types of machines. These are not described in detail herein, because they are readily available elsewhere. Anyone who learns to work such a machine will learn how to control and vary each of a number of different parameters, including fill density, fill stitch length, primary underlay density and stitch length, secondary underlay density and stitch length, primary underlay angle, speed (in stitches per minute), and run fill/feed. If an operator understands those parameters, and understands how the products that result are affected, when those parameters are modified, he or she can create stitched segments having the shapes of circles, ovals, polygons, wedges, arcs, etc., and having loops or stitches with controllable heights, densities, and other parameters, using combinations of (i) any selected type of suitable backing layer, and (ii) any selected type of fiber(s) having any desired combination of chemical content, thickness, stiffness, and other traits.
Computer-controlled stitching machines have been used previously to create various types of surgical implants; however, to the best of the knowledge and belief of the inventors herein, none of those implants or reinforcing materials have ever previously been designed or used to reinforce hydrogel materials, in implants designed to repair hyaline cartilage in mammalian joints.
For example, various types of “surgical mesh” are used in implants that do not contain hydrogels. Such materials are sold by companies such as Secant Medical (www.secant.com), and Dupuy Mitek (a subsidiary of Johnson & Johnson, which can be accessed through www.jnjgateway.com). However, those types of meshes tend to be relatively thin and flat materials with loose and open structures, and they are not suited for use as described herein.
Other types of porous fabrics called “velours” are used in surgical implants, to create fiber arrays that will encourage cells to grow into the fabric after implantation. For example, velour materials made of a combination of biodegradable polymers (such as polyglycolic acid) mixed with collagen fibers (usually obtained from processed cowhide) are used for blood vessel grafts. These implants encourage ingrowth by endothelial cells, which then secrete enzymes that gradually dissolve and resorb the velour material, while the cells replace the fibrous scaffolding with normal collagen protein, to create regenerated blood vessel tissue. These types of vascular grafts are made and sold by companies such as Boston Scientific. However, those types of velour materials are not suited for use in the types of implants described herein, which have very different structural and operating requirements.
Specialty companies (such as Ellis Developments, Ltd., which describes and illustrates its products at its website, www.ellisdev.co.uk) have developed various types of embroidered implant devices, for purposes such as reconstructive shoulder surgery, hernia repairs, etc. Using a method that was initially developed to create doilies and other items that have an “open” look, these implants are created by using a “base fabric” that can be dissolved and removed after a stitching operation has been completed. For example, by using a backing layer made of a paper-like cellulose derivative (or some other material with a chemical structure different from the threads that create the stitches), it is possible to use detergents, solvents, or hot water to remove the base material, leaving behind an embroidered item with any desired two-dimensional shape. These and other types of thin and flat surgical implants are described and illustrated in McQuaid 2004, U.S. Pat. No. 6,899,728 (Phillips et al 2005), and PCT application WO99/37242 (Phillips et al).
Embroidered and other textiles that have been developed and tested for various medical uses are reviewed in items such as Karamuk et al 2000, McQuaid 2004, and Ellis 2000, and companies that specialize in designing and creating such textiles include Ellis Developments (www.ellisdev.co.uk) and Sew Fine LLC (www.alsew.com).
However, to the best of the inventors' knowledge and belief, none of the items created previously for other medical purposes (such as blood vessel grafts, tendon or ligament repair, etc.) are suited for creating 3D fiber arrays that will have the types of relatively open structures with consistent thickness that will be needed for optimal reinforcement of hydrogel layers, in implants designed to replace the relatively thin hyaline cartilage layers that cover certain bone surfaces.
In addition, to the best of the knowledge and belief of the inventors herein, none of the stitched implant devices created in the prior art have been created in ways that are designed to enable such implants to be securely anchored to hard bone surfaces that may be subjected to thousands or even millions of cycles of compressive and shearing stresses, when used to replace hyaline cartilage in a knee or other joint.
Accordingly, one object of this invention is to disclose that certain types of stitched structures, adapted from textile embroidering, carpet tufting, and similar manufacturing methods, can be adapted to provide 3D fiber arrays that are well-suited for reinforcing hydrogel implants for replacing hyaline cartilage.
Another object of this invention is to disclose that certain types of computer-controlled machines, initially developed to manufacture tufted or sewn materials, can be adapted to provide stitched 3D fiber arrays that can strongly and efficiently reinforce hydrogel implants designed to repair hyaline cartilage.
Another object of this invention is to disclose that computer-controlled stitching machines are ideally suited for creating low-cost reinforced hydrogel samples and prototypes that can be tested in an escalating series of in vitro tests, animal tests, and human clinical trials, during the development and optimization of stitching patterns and parameters that can provide optimal reinforcement for the hydrogel components of implants for replacing hyaline cartilage.
Another object of this invention is to disclose surgical implants having hydrogel components reinforced by stitched 3D fiber arrays, in structures that are well-suited for strong and permanent anchoring to hard bone surfaces in joints that are subjected to high loadings and stresses, such as knees.
Another object of this invention is to disclose flexible surgical implants having reinforced hydrogel components that are designed to replace entire segments of relatively thin hyaline cartilage, rather than merely providing plug-type inserts that will create articulating surfaces that have undesired gaps, crevices, and other discontinuities that are likely to cause abrasion over a span of years.
Another object of this invention is to disclose methods for shaping the upper ends of tufting or pile fibers that reinforce a hydrogel material, and that emerge from a backing layer in a perpendicular orientation, into an alignment that is parallel with (and tangential to) a hydrogel surface in a surgical implant.
These and other objects of the invention will become more apparent through the summary, drawings, and detailed description.